1. Field of the Invention
The present invention relates to engine-driven power generators, in particular, to an engine-driven power generator of a type that uses synchronous power generator in which the operation state corresponding to the power generator load can be appropriately selected by controlling the revolution.
2. Description of the Related Art
In the engine-driven power generator of a type that drives the synchronous power generator with an engine, the engine revolution n, the output frequency f, and the number of magnetic poles P have a relationship expressed as n=120f/P. Therefore, the engine revolution must be maintained at a predetermined value in order to maintain the output frequency at a predetermined value. For example, when the number of magnetic poles is “2”, the engine revolution must be maintained at 3000 rpm at the output frequency of 50 Hz, and the engine revolution must be maintained at 3600 rpm at the output frequency of 60 Hz.
A mechanical governor is generally used in controlling the engine revolution. The mechanical governor detects the engine revolution as centrifugal force, and opens or closes a throttle of a carburetor using a link mechanism and a spring. The mechanical governor easily produces aging change as it is mechanical, and offset adjustment, adjustment of revolution setting or the like are difficult.
Recently, an inverter type power generator is being widely used in which the output frequency of the power generator is controlled with an inverter so that the output frequency does not depend on the engine revolution, and the engine revolution is variably controlled with an electronic governor in place of the mechanical governor with respect to change in the load of the power generator (see e.g., Japanese Patent Publication No. 3540152)
However, the inverter type power generator disclosed in Japanese Patent Publication No. 3540152 has a problem in that it is less likely to become popular since the manufacturing cost is significantly high compared to the synchronous power generator.